1. Field of the Invention
This invention relates to compounds containing a partial ester of an oxirane (epoxy) group and related halogen-containing polymer compositions, preferably poly(vinyl halide) compositions; and more particularly, this invention relates to partial esters of oxirane compounds in stabilized poly(vinyl chloride) (PVC) compositions.
2. Description of Related Art
Many halogen containing polymers and copolymers are thermoplastic in nature and require heating in order to fabricate them in operations such as molding, calendering, and extruding. The heat with which these polymers are processed is usually in the range of 140.degree. C. to 250.degree. C., and more typically 150.degree. C. to 225.degree. C. and is limited in degree and duration by their tendency to deteriorate and decompose. Decomposition of the polymers leads to deterioration of the resultant physical properties of the resin. In addition, a severe darkening in color of the resin results which prohibits its use in lightly colored or transparent articles. This deterioration and decomposition is a major drawback to the use of poly(vinyl chloride) resins in many applications. In order to overcome this deficiency thermal stabilizers, lubricants and processing aides are employed with halogen containing vinyl polymers.
Sarvetnick, Polyvinyl Chloride, Van Nostrand Reinhold CO., pp. 124-127, 1969, discloses the use of both external and internal lubricants in PVC. The main purpose of a lubricant compound is to facilitate processing and permit control of processing rate. External lubricants cause lubricity between the composition and metal surfaces of molds and processing equipment. Internal lubricants affect the frictional properties of resin particles in the composition during processing, thus enabling the compounder to maintain control over the fusion rate of the resin. Most lubricants exhibit both internal and external properties; however some are quite specific. Stearic acid and metal stearates are most commonly used. Other lubricants employed include petroleum based waxes, mineral and vegetable oils, low molecular weight polyethylene, amide and ester waxes, and silicone oils. Metal stearates such as lead, barium, cadmium, and calcium may be used for the dual purpose of stabilizing and lubrication. Lubricants are typically used in the range of from 0.25 to 1.0 percent.
In general, stabilizers fall into three main classes, metal soaps, organic chemicals, and organometallic compounds. Vinyl halide polymer compositions typically contain one or more metal-containing heat stabilizers. Metal-containing stabilizers include compounds where the metal is lithium, sodium, potassium, magnesium, calcium, zinc, strontium, cadmium, barium, manganese, iron, cobalt, titanium, aluminum, tin, lead, bismuth or antimony, or a mixture of any two or more such metal-containing compounds The use of many of these metal-containing compounds as PVC stabilizers is described in British Patent Specification 1,001,344 and an article by Robert G. Weiler, "Uncommon Metals as Heat Stabilizers for Flexible Vinyl", pages 534-537, Volume 28, Technical Papers, Society of Plastics Engineers, Inc., 1982.
Organotin compounds, particularly those having tin bonded to sulfur, such as those which contain a mercapto group, have been found to be an extremely effective type of stabilizer for halogen containing polymers, such as poly(vinyl chloride) polymers. A continuing goal of the fabricator is to reduce the cost of the compositions but obtain equal or better heat stability properties. This may be achieved with lower usage of more efficient organotin stabilizers but they still are relatively expensive. Another approach is to replace at least a portion of the tin present in a given resin formulation with a less expensive material, e.g., by addition of less expensive synergistic additive compounds.
Other well-known metal-containing heat stabilizers for vinyl halide polymers include compounds of the elements of Groups IIA and IIB of the Periodic Table of the Elements, as well as compounds of tin, lead, bismuth and antimony. Conventional well-known heat stabilizers for vinyl chloride polymers are also discussed in Chapter 9 of The Encyclopedia of PVC, edited by L. I. Nass (M. Dekker, New York 1976).
Japanese Patent, JP 75-143456 discloses a stabilized composition of a halogen resin containing a reaction product of a trihydric alcohol or greater and an epoxidized fatty acid ester. The composition contains at least one metallic salt which can be organotin or Group IIa metal stabilizing compound. While not identifying the structure of the reaction product, the Japanese reference discloses that the compound can be synthesized in water or in a water soluble organic solvent with an inorganic acid or alkaline catalyst. This would be expected to result in significant hydrolysis or saponification of the ester and possibly cleavage of the epoxy group. Therefore, the composition of the reaction products is not apparent